DIY IRF610 MOSFET Class-A Headphone Amplifier Project

Not thrilled with how a computer soundcard drove my 32 ohm Grado SR80 headphones, I decided to build myself a desktop headphone amplifier for the office. In this instance I had plenty of voltage gain, but the sound card just runs out of gas with good headphones. This amplifier will only be suitable in setups where the input signal does not require

voltage amplification (such as the output of a preamplifier, mp3 player or computer). This amplifier will delivery plenty of current to drive more demainding headphone types. This is a simple do-it-yourself (DIY) headphone amplifier project that is fashioned primarily after the Class-A MOSFET Headphone Driver project by Greg Szekeres and to some extent Mark`s DIY Class-A 2SK1058 MOSFET Amplifier Project. The amplifier concept is simple and follows a typical single-ended class-A circuit utilizing an active constant current source (CCS) in place of a passive resistor. A CCS doubles the efficiency of the circuit over that where a passive load resistor is used, bringing it to a maximum of 25%. There are a couple of items to note. A FET follower circuit will be able to supply high current, but the voltage gain will be less than one. This amplifier will only be suitable in applications where the input signal does not require voltage amplification (such as the output of an mp3 player or computer). Also, a simple single-ended circuit like this will have no power supply ripple rejection and thus any noise in the power supply is going to go right through amplifier. For that reason, you will need to use a regulated power supply. Suitable inexpensive regulated (wall wart) power supplies can be purchased from Radio Shack. 10-20VDC and 750mA should be fine. The schematic for this headphone amplifier project is shown below in Figure 2....

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